Telephone service providers are committed to providing high data rate services to customers. This requires the location of power consuming equipment near the customer-end and necessarily outside of the battery-backed Central Office environment. One way to deliver power to remote sites without interruptions is to use uninterruptible power delivered from the Central Office at elevated voltages over several pairs of telephone lines that are configured in parallel.
This approach allows accommodation of battery maintenance, efficiency and issues involving “reach” but leaves the power distribution susceptible to latent failures since a portion of the parallel wiring may be lost with no clear indication to network managers. In these cases, the conductor or insulation may degrade or fail open on one or more of the wires that are paralleled to deliver the remote power. It is advantageous to detect this failure quickly to maintain delivery performance.
In a remote power circuit that uses two or more telephone wiring pairs, the failure of one wire would typically produce a measurable increase in transmission resistance associated with power transmission. However, in other situations, there are large regions of operation where even significant changes in conductor resistance may produce only small measurable changes in source current since the dependence of source current on line resistance is weak. To make this more troublesome, the field environment where these current measurements must be taken is often rich in electrical noise, and a measurement converter used is typically not as accurate as a laboratory quality measurement or meter. Additionally, the load may have some traffic dependence that will contribute to changes in current that is normal.
In a typical high-reliability installation, the downstream power converter will be provided with redundant power, such that a load will not suffer if one power feed is delivering slightly less than before. Yet, degradation of insulation or wiring or failure of a single wire or wiring pair may remove redundant power without providing any warning. This latent failure is unacceptable to any service provider who counts downtime in minutes per year.
Accordingly, what is needed in the art is an enhanced way to determine latent or actual failures of telephone wiring pairs employed for power distribution.